1. Field of the Invention
The present invention relates to a MOSFET (i.e., an insulated gate type field effect transistor), and more particularly to a trench dual-gate MOSFET (hereinafter referred to as "TDMOSFET").
2. Description of the Related Art
It is well-known to fabricate a vertical MOSFET by utilizing a projection which is defined by a trench formed in selected portions of a semiconductor substrate. Such a TDMOSFET-fabricating technique is disclosed in, e.g., T. Mizuno et al., "High Speed and Highly Reliable Trench MOSFET with Dual-Gate." Symp. VLSI Dig., pp 23-24, 1988.
However, the TDMOSFET shown in the document has restrictions in actual application. For instance, if the channel width of that TDMOSFET is increased for the improvement of the current driving ability, a wide area will be required for forming the TDMOSFET on a chip. Since the density of integration on the chip is thus adversely affected, the TDMOSFET of the document is not suitable for use as a transistor required of an high current driving ability.